So and now another answer without "believing, thinking, not knowing and guessing":

You can easily couple several dimmer switches to one lamp and also several lamps to one dimmer switch or both together without the need for a bridge.

I have 3 Hue White on 3 dimmer switches in each of 3 rooms here, without having a bridge or similar anywhere. Simply pair switch 1 with bulb 1, then with bulb 2, then with bulb 3. Then pair switch 2 with lamp 1, then with lamp 2, then with lamp 3. Then the same again for switch 3. Has worked for many years without problems.

Before I bought it, I even asked the Philips service if it was possible and they told me the number of possible combinations. Unfortunately, I no longer have the answer here, but it was in the range of significantly more pieces (both dimmers per lamp and lamps per dimmer), so I simply bought and set up.

Hello JörgV378,
As far as I know, all devices must at least be connected via some bridge and are thus accessible in the app. This is like a kind of router from which everything is controlled.
In my opinion, the dimmer switch must also be coupled via a bridge.
Example: I have 1 bridge for everything in the house. There are 3 rooms each with 4 lamps incl. dimmer switch, one room even via e27 socket (spotlight). I have coupled one room with 2 dimmer switches for manual access upstairs/downstairs.
With Bridge it should work for sure.
REGARDS

Hello Jörg
Unfortunately I cannot answer your question conclusively.
I use a dimmer switch together with a bridge.
However, I suspect that your setup with 2 switches on one lamp is not possible.